How Scientists Determine Temperature Records and Dangerous Heat Waves
A temperature record is set when the reading at a specific weather station exceeds the previous high for that day, month, or season. For regional and global records, scientists combine data from land-based weather stations, ships, and ocean buoys and calculate average values, according to Deutsche Welle.
The oldest continuous temperature record—the Central England Temperature Data Series—dates back to 1659. At the same time, the three most comprehensive global datasets used to determine the warmest years have been systematically collected since 1880. They are maintained by the U.S.-based Goddard Institute for Space Studies and the National Centers for Environmental Information, as well as the U.K.’s Met Office Hadley Centre.
To reconstruct the climate before the advent of thermometers, researchers use so-called climate archives: ice cores, tree rings, ocean sediments, and fossils. The most complete continuous ice core from Antarctica spans over a million years and contains ancient air bubbles that allow scientists to measure past levels of carbon dioxide in the atmosphere.
Climatologists distinguish long-term changes from normal weather fluctuations by analyzing data over decades and applying statistical methods and climate models. NASA, NOAA, and the Copernicus Climate Change Service use different methodologies and datasets, but have reached the same conclusion regarding the warming trend: the last decade included the warmest years on record since instrumental observations began.
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The impact of climate change on extreme events is also assessed using attribution studies. These studies compare the probability and intensity of a specific event in the current climate with a simulated world without human-induced warming. In a study of the June 2026 heatwave in Europe, the World Weather Attribution group called it the strongest on record for the region under study.
Air temperature does not always reflect the full impact of heat on the body. High humidity hinders sweat evaporation, making it harder for the body to cool down. Wet-bulb temperature is also used to assess heat stress: when wet-bulb temperatures remain around 35°C for extended periods, the body can overheat even in the shade and with adequate water intake. Dry heat can also be dangerous due to the risk of dehydration.
Cities are often warmer than rural areas due to the urban heat island effect. Roads, buildings, and other hard surfaces absorb and store heat, while trees and other vegetation cool the area through shade and evaporation. Dense development and narrow streets also impair air circulation. This effect can be mitigated by trees, parks, green roofs, reducing the density of paved surfaces where possible, and lighter-colored building materials that better reflect sunlight.
